I want to access virtual consoles in my Ubuntu guests running VirtualBox with Ubuntu guest. However, even if the focus is within the guest window, if I press Ctrl+F1 thru F6 I move in a virtual terminal of the host, not the guest.

Also for those who are running Virtual Box on Mac OS, remember to press the fn key in addition to the Host since it is the key to toggle F1 through F12 functionality on Mac OS. So the combination becomes Host + fn + F1 through F12.